The field of the invention pertains to means for delaying acoustic signals generated by electroacoustic drivers or transducers in sound reproduction speakers. In particular, the invention pertains to means for assuring the simultaneous receipt of sounds by the listener generated by simultaneous electric signals input to the speaker.
Typically, the electroacoustic drivers are mounted in apertures in a baffle forming a portion of the speaker cabinet. Unfortunately, electric signals impressed upon two or more of the drivers simultaneously will not create a simultaneous acoustic signal at the position of the listener. In practice the low frequency filter and low frequency driver exhibit more delay than the high frequency filter and high frequency driver. Therefore, prior art efforts involve adding delay to the air path of the high frequency driver. Air path delay techniques are disclosed in U.S. Pat. Nos. 3,824,343 and 3,927,261 wherein a plurality of drivers are physically positioned to provide increased air paths in proportion to the rise times of the drivers. Similarly, U.S. Pat. No. 4,015,089 discloses a plurality of drivers arranged in staggered relation along their radiating axes at a predetermined spacing from each other. A second approach to delay, disclosed in the prior art, pertains to active electrical network means. U.S. Pat. No. 4,151,369 discloses a decoder, gain and delay system for multiple speakers in a "surround sound" configuration. The speakers are located circumferentially about the listener at various radii.
Another approach to active networks is disclosed in a series of articles by Siegfried Linkwitz entitled "Loudspeaker System Design" published in WIRELESS WORLD, May and June 1978 issues. Linkwitz describes active crossover networks with active delay compensation. He comments that the design flexibility of active networks outweighs the cost saving of a passive network, however, no passive network is disclosed. He further emphasizes at the end of his series of articles that computer optimization would be required to design a passive network comparable to his active crossover networks.